Dual film light guide for illuminating displays

ABSTRACT

A front light guide panel including a plurality of embedded surface features is provided. The front light panel is configured to deliver uniform illumination from an artificial light source disposed at one side of the font light panel to an array of display elements located behind the front light guide while allowing for the option of illumination from ambient lighting transmitted through the light guide panel. The surface embedded surface relief features create air pockets within the light guide panel. Light incident on the side surface of the light guide propagates though the light guide until it strikes an air/light material guide interface at one on the air pockets. The light is then turned by total internal reflection through a large angle such that it exits an output face disposed in front of the array of display elements.

BACKGROUND

1. Field of the Invention

The present invention relates generally to frontlit displays, such asLCD displays, and particularly to dual film configurations of lightguides for frontlit displays.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and/or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY

Various embodiments described herein comprise light guides fordistributing light across an array of display elements. The light guidemay include surface relief features to turn light propagating in a lightguide onto the array of display elements. The surface relief featuresmay comprise facets that reflect light. To protect these facets, thefacets are embedded within the light guide. Other embodiments are alsodisclosed.

One embodiment of the invention comprises a light guide comprising anupper portion having top and bottom surfaces and a lower portion havingtop and bottom surfaces. The bottom surface of the upper portion iscontoured. The top surface of the lower portion is also contoured. Theupper portion is disposed over the lower portion such that the contouredbottom surface of the upper portion and the contoured top surface of thelower portion form cavities between the upper portion and the lowerportion.

Another embodiment of the invention comprises a light guide comprising acover layer having top and bottom surfaces, a film having top and bottomsurfaces wherein the top surface of the film is contoured, and a lightguide plate having top and bottom surfaces. The cover layer is disposedover the film such that the bottom surface of the cover layer and thetop contoured surface of the film form cavities between the cover layerand the film. The film is disposed between the cover layer and the lightguide plate.

Another embodiment of the invention comprises a light guide comprising acover layer having a planar surface, a film having first and secondsurfaces, and a light guide plate having top and bottom planar surfaces.The first surface of the film comprises a plurality of concave surfacerelief features and the second surface of the film is planar. The filmis disposed on the light guide plate such that the planar second surfaceis adjacent the light guide plate and the concave surface relieffeatures of said first surface face away from the light guide plate. Thecover layer is disposed adjacent the film such that the planar surfaceof the cover layer and the concave surface features of the film formcavities between the cover layer and the film.

Another embodiment of the invention comprises a light guide comprising afirst means for guiding light and a second mean for guiding light. Thefirst and second light guiding means have respective means for matingthe first and second light guiding means together. The mating means forboth the first and second light guiding means is contoured such thatwhen the first and second light guiding means are mated together. Themeans for reflecting light are formed therebetween.

Another embodiment of the invention comprises a light guide comprising afirst means for guiding light, a second means for guiding light, andmeans for covering the second light guiding mean. The covering means isdisposed such that the second light guiding means is between thecovering means and the first light guiding means. The second lightguiding means and the covering means have respective means for matingthe second light guiding means and the covering means together. Themating means for the second light guiding means is contoured such thatwhen the second light guiding means and the covering means are matedtogether, means for reflecting light are formed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIG. 5A illustrates one exemplary frame of display data in the 3×3interferometric modulator display of FIG. 2.

FIG. 5B illustrates one exemplary timing diagram for row and columnsignals that may be used to write the frame of FIG. 5A.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 depicts a front light guide unit for use in a flat panel displaycomprising a linear light source and a front light guide panel.

FIG. 9 depicts a frontlit display comprising a reflective display panel,a dual film front light guide panel having embedded surface features anda light source.

FIG. 10 depicts the top and bottom films of the dual film light guide ofFIG. 9.

FIG. 11 depicts light rays from the display panel propagating throughthe light guide of FIG. 9.

FIG. 12 depicts light rays from ambient light propagating through thelight guide to the display panel.

FIG. 13 depicts an alternative embodiment of a front light guide whereinthe distance between surface features varies across the length of thelight guide.

FIG. 14 depicts an alternative embodiment of a front light guide havingembedded surface features.

FIG. 15 depicts an alternative embodiment of a frontlit displaycomprising a reflective display panel, a front light guide panel havingembedded surface features and a light source.

FIG. 16 depicts an alternative embodiment of a front light guide havingembedded surface features.

FIG. 17 depicts light rays incident on one of the embedded surfacefeatures of the front light guide of FIG. 16.

FIG. 18 depicts an alternative embodiment of a front light guide havingembedded surface features with a reflective coating.

FIG. 19 depicts a detailed view of a portion of an alternativeembodiment of a front light guide showing multifaceted embedded surfacefeatures.

FIG. 20 depicts a detailed view of a portion of an alternativeembodiment of a front light guide showing embedded surface features withcurved facets.

FIG. 21 depicts an alternative embodiment a frontlit display comprisinga reflective display panel and a front light guide panel having embeddedsurface features, wherein the embedded surface features are disposed ona side of a film facing the light guide panel.

FIG. 22 depicts an alternative embodiment of a frontlit display similarto that of FIG. 21 wherein the embedded surface features have verticalwalls.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout.

In various embodiments described herein, an edge illuminated front lightguide panel includes a plurality of embedded surface features. Theembedded surface relief features may form fillable gaps or cavities suchas air pockets within the light guide panel. Light injected into an edgeof the light guide propagates though the light guide until it strikes anair/light guide material interface at one on the air pockets. The lightis then turned by total internal reflection through a large angle suchthat it exits an output face disposed in front of a display panel. Tocreate air pockets, a pair of guide portions have contoured surfacesthat are contacted to each other. Other embodiments are also disclosedherein.

As will be apparent from the following description, the embodiments maybe implemented in any device that is configured to display an image,whether in motion (e.g., video) or stationary (e.g., still image), andwhether textual or pictorial. More particularly, it is contemplated thatthe embodiments may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,wireless devices, personal data assistants (PDAs), hand-held or portablecomputers, GPS receivers/navigators, cameras, MP3 players, camcorders,game consoles, wrist watches, clocks, calculators, television monitors,flat panel displays, computer monitors, auto displays (e.g., odometerdisplay, etc.), cockpit controls and/or displays, display of cameraviews (e.g., display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures, packaging, and aesthetic structures (e.g., display of imageson a piece of jewelry).

The display device, such as, e.g., interferometric modulating MEMSdevices, LCDs, etc., may include a light source that is configured tolight an array of display elements to an appropriate level for viewing.In combination with the light source, a light guide may be coupled tothe array of display elements proximate the light source to distributelight across the array of display elements. Light guides may bepositioned in various orientations with respect to the display elements,such as behind the display elements, e.g., a backlight, or in front ofthe display elements, e.g., a frontlight. In the systems and methodsdescribed herein, a front light guide panel is disposed in front of thearray of display elements to deliver uniform illumination from anartificial light source to the array of display elements while allowingfor the option of illumination from ambient lighting via a reflectivelayer in the display elements.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical gap with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent, and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack 16 are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the gap 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5B illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. Thus, there exists awindow of applied voltage, about 3 to 7 V in the example illustrated inFIG. 3, within which the device is stable in either the relaxed oractuated state. This is referred to herein as the “hysteresis window” or“stability window.” For a display array having the hysteresischaracteristics of FIG. 3, the row/column actuation protocol can bedesigned such that during row strobing, pixels in the strobed row thatare to be actuated are exposed to a voltage difference of about 10volts, and pixels that are to be relaxed are exposed to a voltagedifference of close to zero volts. After the strobe, the pixels areexposed to a steady state voltage difference of about 5 volts such thatthey remain in whatever state the row strobe put them in. After beingwritten, each pixel sees a potential difference within the “stabilitywindow” of 3-7 volts in this example. This feature makes the pixeldesign illustrated in FIG. 1 stable under the same applied voltageconditions in either an actuated or relaxed pre-existing state. Sinceeach pixel of the interferometric modulator, whether in the actuated orrelaxed state, is essentially a capacitor formed by the fixed and movingreflective layers, this stable state can be held at a voltage within thehysteresis window with almost no power dissipation. Essentially nocurrent flows into the pixel if the applied potential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4, 5A, and 5B illustrate one possible actuation protocol forcreating a display frame on the 3×3 array of FIG. 2. FIG. 4 illustratesa possible set of column and row voltage levels that may be used forpixels exhibiting the hysteresis curves of FIG. 3. In the FIG. 4embodiment, actuating a pixel involves setting the appropriate column to−V_(bias), and the appropriate row to +ΔV, which may correspond to −5volts and +5 volts, respectively Relaxing the pixel is accomplished bysetting the appropriate column to +V_(bias), and the appropriate row tothe same +ΔV, producing a zero volt potential difference across thepixel. In those rows where the row voltage is held at zero volts, thepixels are stable in whatever state they were originally in, regardlessof whether the column is at +V_(bias), or −V_(bias). As is alsoillustrated in FIG. 4, it will be appreciated that voltages of oppositepolarity than those described above can be used, e.g., actuating a pixelcan involve setting the appropriate column to +V_(bias), and theappropriate row to −ΔV. In this embodiment, releasing the pixel isaccomplished by setting the appropriate column to −V_(bias), and theappropriate row to the same −ΔV, producing a zero volt potentialdifference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding and vacuum forming. In addition, the housing 41 may be made fromany of a variety of materials, including, but not limited to, plastic,metal, glass, rubber, and ceramic, or a combination thereof. In oneembodiment, the housing 41 includes removable portions (not shown) thatmay be interchanged with other removable portions of different color, orcontaining different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43, which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g., filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment, the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS, or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, or a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some embodiments, control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some embodiments, controlprogrammability resides in the array driver 22. Those of skill in theart will recognize that the above-described optimizations may beimplemented in any number of hardware and/or software components and invarious configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the gap, as in FIGS. 7A-7C, but the deformable layer 34does not form the support posts by filling holes between the deformablelayer 34 and the optical stack 16. Rather, the support posts are formedof a planarization material, which is used to form support post plugs42. The embodiment illustrated in FIG. 7E is based on the embodimentshown in FIG. 7D, but may also be adapted to work with any of theembodiments illustrated in FIGS. 7A-7C, as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

In display technology, artificial lighting can be used to make thedisplay visible. To do this, light from a source such as a fluorescenttube or LED is captured into a thin slab shaped light guide and isdelivered to the display. The illumination can be provided by“backlighting” or “frontlighting.”

Flat panel displays are typically “backlit” by light guide slabs (oftenreferred to as “backlights”) that redirect light from a linear lightsource to transmit uniform illumination to the rear surface of thedisplay panel. The light injected along an edge of the light guide panelis guided within the light guide panel and extractor features located ona rear or front surface of the light guide panel can be used to disruptthe propagation of the light within the light guide panel and cause thelight to be uniformly ejected across the front surface of the paneltoward the display.

Alternatively, flat panel reflective displays may be “front-lit” by afront light guide that delivers uniform illumination from the viewingside of the display panel. Such displays may also reflect ambient light,thereby increasing their brightness in well-lit ambient lightconditions. The frontlight may be utilized only in low-light ambientconditions in some configurations.

In a frontlit system, as shown in FIG. 8, light from a linear source 2such as a fluorescent tube, LED or LED array, or a light bar illuminatedby an LED is injected into a thin slab shaped light guide panel 1003located in front of the display panel 4.

The light 5 injected into the light guide is guided along the length ofthe light guide 1003. In order to provide uniform illumination to thedisplay panel, the light 5 is turned through a large angle,approximately ninety degrees, such that it propagates through thethickness of the light guide 1003 and escapes through the output face1031. The light turning may be accomplished via a surface reliefstructure containing a plurality of turning features.

As discussed above with respect to FIG. 8, light beams 5 entering thelight-input surface 1033 are propagated through the front light guide 3toward the opposite side face of the light guide 1003 by total internalreflection. The viewing face 1032 further contains a plurality of lightturning structures such as prismatic microstructures 1040 arranged in apattern along the width of the viewing face 1032. The prismaticmicrostructures 1040 may comprise two or more turning facets 1042 and1044 angled with respect to one another for reflecting the light at thefacet/air interface, causing the light to be turned through a largeangle. The plurality of pairs of adjacent facets 1042 and 1044 maycomprise, for example, one shallow, long facet and a much shorter butmore steeply inclined facet. If light strikes the first, shallow facetand then the second steeper facet sequentially as shown in FIG. 8, totalinternal reflection occurs at both facet/air interfaces and the lightturns through large angles. The light following this path is thenextracted out of the light guide through the output face towards theadjacent display panel. Thus, the light beams 5 encountering one ofthese structures 1040 are diffusely or specularly reflected, and largelyemitted through the output face 1031. Multiple internal reflectionsenhance mixing of light within the light guide plate 3 which assists inproviding uniformity in light output across the light output face 1031.

These prismatic surface relief features are either fabricated into thesurface of the light guide, such as by embossing, injection moldingcasting or other techniques, or are fabricated into a thin film that is,in turn, attached to the surface of a planar light guide. In certaindesigns, the prismatic surface relief structure is located on the topsurface of the light guide, i.e. the exposed surface opposite the lightoutput face. As a result, if not protected from ambient conditions, theturning facets are vulnerable to contamination from dirt, water or othercontaminants. The presence of, for example, dirt may destroy totalinternal reflection at the facet interface and reduces the light turningperformance of the prismatic microstructure. Dust or particlecontaminates trapped in the valleys of such prismatic microstructurewill also scatter light directly into the viewers eye and thereforereduce display contrast.

Thus, it is advantageous to protect the prismatic surface reliefstructure during both the manufacture and the lifetime use of thedisplay. This is a major problem and has restricted the widespreadapplication of this technology. Clean room facilities may be used toprevent surface relief contamination during manufacture; but thisapproach increases manufacturing costs. In addition, a sealed coverplate may be used to protect the prismatic surface during device use.However, this contributes to the thickness of the light guide and thecomplexity of manufacturing. Accordingly, other designs, which may yieldperformance enhancements, simplify manufacturing, and/or reduce cost,may be desirable.

FIG. 9 shows an example front-lit display, comprising a linear lightsource 2 and a front light guide panel or plate 103 (LGP). This linearlight source 2 may comprise, for example, a cold cathode fluorescenttube (CCFL) lamp, an LED, an OLED, a light bar illuminated by an LED orLED array, a fluorescent tube or any other suitable linear light source.This light source 2 is aligned parallel with an edge of the front lightguide plate 103 such that light from the linear light source 2 isincident on a light-input surface 133 of the light guide plate 103.

The front light guide 103 comprises a substantially opticallytransmissive material capable of redirecting and uniformlyredistributing light from the linear light source 2 over the planarsurface of an output face. The light guide 103 comprises a light inputsurface 133, a light output face 131 perpendicular to the light inputsurface, and a viewing face 132 opposite the light output face 131.

The light 5 from the linear light source 2 enters the light inputsurface 133 of the light guide plate 103 and as will be explained inmore detail below, propagates along the length L of the light guideplate 103 reflecting between the front and back faces 132 and 131 of thelight guide plate 103 and is turned by features within the light guideplate 103 to exit the light guide plate 103 through the light outputface 131 and propagate toward the display panel 4.

In certain embodiments, the front light guide 103 comprises arectangular shaped plate or sheet with the output face 131 and viewingface 132 being parallel to each other. In one embodiment, the frontlight guide 103 may comprise a wedge shaped plate wherein the lightoutput face 131 and viewing face 132 are angled with respect to oneanother. In another embodiment, portions of the light output face 131and viewing face 132 are angled with respect to one another and otherportions are parallel to one another. In another embodiment, the lightoutput face 131 and viewing face 132 are not parallel to each other, forexample the viewing face 132 may have a sawtooth pattern (not shown).

In certain embodiments, the front light guide may be comprised of anupper portion and a lower portion each having contoured surfaces whichare joined together such that the facing contoured surfaces create aplurality of turning features embedded between the upper and lowerportions. For example, as shown in FIG. 9, the front light guide 103 maybe comprised of two polymer films 136 and 138 joined together such thatthe light turning features 140 of the light guide 103 reside on the twoadjacent faces of the polymer films 136 and 138 and are thus embedded inthe resulting light guide panel 103.

As shown in more detail in FIG. 10, the light guide 103 includes thebottom film 136 (positioned farther from the viewer) and the top film138 (positioned closer to the viewer). The bottom film 136 has a flatplanar surface that forms the output face 131 of the resulting lightguide plate and an opposing structured surface 135 that includes aplurality of surface relief features 140 a spaced apart across the widthof the film 136. Likewise, the top film 138 comprises a flat planarsurface that forms the viewing face 132 of the resulting light guide 103and an opposing structured surface 137 that includes a plurality ofsurface relief features 140 b spaced apart across the width of the film138. A light guide plate 103 may be created by joining the two films 136and 138 together with their structured sides 135 and 137 facing oneanother such that the surface features 140 a and 104 b become embeddedin the resulting film 103 and are thereby protected from outside damageor contamination. In the illustrated embodiment, the films 136 and 138are optically coupled such that when each of the structured faces 135and 137 of the films 136 and 138 are aligned and joined together, thesurface relief features 140 a and 140 b form a series of fillable gapsor cavities 150 (see FIG. 9) spaced apart across the length of the lightguide plate 103. However, in alternative embodiments, the opposingsurface features 140 a and b may not be equally spaced along thesurfaces 135 and 137 of the top and bottom films 136 and 138 and may beinstead intentionally offset, for example, to provide for differentlight turning effects along the length of the light guide plate.

In one embodiment, the top and bottom films 136 and 138 have the sameindex of refraction such that, when joined, they become optically onelight guide, operating like one film, with no optical interfacetherebetween and a plurality of cavities embedded therein. In use,guided light striking an interface between one of the facets and theembedded air pocket will preferentially undergo total internalreflection at that interface and thereby be turned though a large angle,for example between 75°-90°. In certain embodiments, the cavities may befilled with a filler material to provide mechanical stability andstrength to the light guide plate. The filler material may have adifferent index of refraction from the light guide material to ensurethat total internal reflection at the facet/cavity interface stilloccurs.

Accordingly, the cavities may be open. As described above, thesecavities may also be filled with material. The term cavity is used todescribe either case, when the volume is open, e.g. filed with air orgas, and when the volume is filled with material such as an opticallytransmissive material having a different optical property, such asrefractive index.

The shape and size of the surface features 140 a and 140 b, and thus theresulting cavities 150 (see FIG. 9), may also be chosen to interactextensively with guided light incident on the input face and to increaseor maximize extraction efficiency, for example, to provide uniformdistribution of light at a desired angle across the output face.Accordingly, the surface features 140 a and 140 b may comprise anysuitable shape for causing light injected from the side, input face 133that is generally parallel to the output face 131 to be turned over alarge angle and ejected from the output face 131. At the same time thesurface features 140 a and 140 b may be shaped to permit light incidenton the viewing face 132 such as ambient light that is substantiallynormal to the viewing face 132 to be transmitted through the light guideplate 103 and the surface features relatively unaffected and ejectedfrom the output face 131 at an angle substantially normal to the outputface. For example, the surface features may comprise a plurality ofrepeating prismatic microstructures each comprising two adjacent,symmetrical facets. Alternatively, the surface features may comprise aplurality of repeating prismatic microstructures each comprising twoadjacent facets having different angles of inclination with respect tothe film. Other configurations are also possible.

In one embodiment, the surface features 140 a and 140 b are sufficientlysmall to be unobtrusive to the viewer. In certain embodiments, thesurface features 140 a and 140 b may be identical across the length, L,of the films 136 and 138, for example repeating the same angularorientation, shape or dimensions as described above. Alternatively, theshape, angular orientation and/or size of the surface features 140 a andb may vary across the length of the films 136 and 138.

In certain embodiments, the surface features 140 a may be mirroropposites of the surface features 140 b, alternatively, the surfacefeatures 140 a may be complementary shapes relative to the surfacefeatures 140 b, one fitting at least partially in the other. When joinedtogether, the surface features 140 a and 140 b form opposing top andbottom films 136 and 138 may create a plurality of symmetrical cavities150 embedded in between the two films. Alternatively, the surfacefeatures 140 a and 140 b from opposing top and bottom films 136 and 138may create asymmetrical cavities embedded between the films. In certainembodiments, such asymmetrical cavities may be designed to reduce thelength of the facet/air interface and thereby reduce the detrimentalFresnel reflections that occur when the light rays strike the interface.Because the cavities are created by the joining of surface features 140a and 140 b, more complex turning features can be created. For example,re-entrant structures may be created where the re-entrant nature is notformed in either film, but rather is created when the surface features140 a and 140 b of the top and bottom films 136 and 138 are joined.

For example, in the illustrated embodiment shown in detail in FIG. 10,the surface features 140 a on the bottom film 136 comprise a pluralityof alternating microprisms 142 spaced apart across the length of thestructured surface 135 and separated by a plurality of planar spacers143. The microprisms 142 are formed of adjacent facets angled withrespect to each other such that light rays 5 incident on the tip of themicroprisms 142 will enter the prism and subsequently be internallyreflected at the microprism/air interface and thereby turned through alarge angle to be ejected from the output face 131 of the light guide103 as light rays 6. The surface features 140 b on the top film 138comprise a plurality of grooves 144 spaced apart across the length ofthe structured surface 137. The grooves 144 comprise adjacent angledsurfaces, having angles with respect to one another such that totalinternal reflection (TIR) rays that are totally internally reflectedacross the length of the film 138, as well light rays with angles closeto TIR, incident on the grooves 144 will be refracted straight acrossthe width of the grooves 144. Thus, as shown in FIG. 9, when the films136 and 138 are conjoined to form light guide plate 103, the surfacefeatures 140 a and 140 b cooperate to form embedded cavities 150, spacedapart along the length of the light guide plate 103. These cavities 150create an air/light guide material interface at the surface of themicroprisms 142 which causes the light traveling through the tip of themicroprisms 142 to be turned through a large angle, thus redistributingand redirecting light rays incident 5 on the input face 133 to beejected as light 6 through the output face 131 and toward the display 4.

In use, as shown in FIGS. 8, 10-11, when light rays 5 from the linearlight source 2 are injected into the front light guide plate 103, thelight rays 5 are propagated through the light guide plate 103 via totalinternal reflection (TIR), an optical phenomenon wherein light travelingfrom a medium with a higher refractive index, such as glass, to one witha lower refractive index, such as air, is incident on the mediumboundary at an angle such that the light is reflected from the boundary.As these light rays are guided through the light guide plate, theyeventually strike the facets of the microprisms 142 of the surfacefeature 140 a. Because of the difference in index of refraction betweenthe air and light guide material at the air/light guide materialinterface formed by the cavities 150, the light rays 5 are turnedthrough a large angle and ejected from the light output face 131 of thelight guide plate 103. The light rays 6 ejected from the light outputface 131 of the light guide plate 103 propagate across an air gap andare incident on the display panel 4, for example an interferometricmodulator display panel, wherein the rays are modulated and reflectedback toward the light output face 131 of the light guide. As shown inFIG. 11, the modulated light rays 7 from the display panel 4 areincident on light output face 131 of the light guide plate 103. Theselight rays 7 are transmitted through the light guide plate 103 and exitfrom the viewing face 132 whereupon they may be seen by a viewer.Accordingly, in various embodiments, the surface features 140 a and 140b, and thus cavities 150, are shaped such that light incident upon thelight output face 131 at normal or near normal angles is transmittedthrough the light guide plate 103 and the cavities 150 without muchdisturbance or deviation.

As shown in FIG. 12, if the ambient light level is sufficiently high,additional illumination from the linear light source 2 may not berequired to illuminate the display panel 4. Here, the ambient light rays8 incident on the viewing face 132 at a normal or near normal angle arelikewise propagated through the light guide plate 103 and cavities 150without much disturbance. The ambient light rays 8 are then ejected fromthe light output face 131 and propagate across an air gap to the display4 as described above. Thus, the light guide plate 103 provides thecapability to interact extensively with the guided light incident on alight input face while at the same time only slightly disturbingnon-guided light incident on the output and viewing faces. In addition,the light guide plate 103 provides protection for the light turningfeatures from damage or contamination by embedding the surface featuresin between two films.

In certain embodiments, the size, shape spacing, or other characteristicof the surface features 140 a and b may be varied across the length, L,of the light guide plate 103, for example to obtain uniform lightextraction across the length of the light output face 131. As shown inFIG. 13, a particular light guide panel 103 (as illustrated in FIGS.9-12) is shown with the distance between pairs of corresponding surfacefeatures 140 a and 140 b varying from 50 to 450 microns across the widthof the light guide plate. For example, in the illustrated embodiment,the spacing between surface features 140 a and 140 b decreases withincreasing distance from the light source 2. For example, in the regionA of the light guide plate 103 closest to the light source 2, thespacing between pairs of surface features 140 a and 140 b is about 450microns; in the middle region B the spacing between pairs of surfacefeatures 140 a and 140 b is about 150 microns; and in the farthestregion C the spacing between pairs of surface features 140 a and 140 bis about 50 microns. The decrease in distance between the pairs ofsurface features 140 a and 140 b results in an increase in extractionefficiency in the regions of the light guide plate 103 furthest from thelight source 2. This extraction efficiency balances out the decrease inlight flux actually reaching father regions of the light guide 103 andresults in a more uniform output across the surface of the light outputface 131. Alternatively, as discussed above, the viewing face 132, ofthe light guide plate 103 may be angled with respect to the output face131 to form a wedged shaped light guide plate 103 which also increasesthe extraction efficiency in the regions of light guide plate furthestfrom the light source 2.

The light guide 103 may be fabricated by imprinting films 136 and 138with a designed surface relief, such as the microprisms 142 on bottomfilm 136 or the faceted grooves 144 on top film 136 depicted in FIG. 10.These surface relief features may be created by embossing, injectionmolding or any other suitable technique known in the art. Once thesurface features have been molded on the top and bottom films, the filmsmay be aligned and joined together to create the light guide plate 103.The films may be joined together, for example, by laminating with anysuitable adhesive. Suitable adhesives may include pressure sensitiveadhesives, heat cured adhesives, UV or electron beam cured adhesives orany other adhesives having suitable optical and mechanical properties.In some embodiments, when laminating the films, however, care must betaken not to fill the open cavities between the surface features withthe adhesive material, thereby possibly destroying the light turningproperties of the cavities. In some embodiments, the films are betweenabout 70-80 microns thick, however the surface features are only betweenabout 7 to 8 microns deep. Therefore, without due care, the laminatingadhesive used to join the top and bottom films may ooze or seep into andfill the open cavities created by the surface features when pressure isapplied to join the films. This result may be avoided by controlling thethickness of the laminating material applied between the top and bottomfilms to prevent excess adhesive. Alternatively, a photo-reactiveadhesive may be used and may be cured by UV light so that excessivepressure on the two films is not required to join the two films.Alternatively, a thin metallic coating may be applied between the twofilms and then cured with RF energy. In certain embodiments, thelaminating material may be applied before the films are imprinted withsurface relief features. When the surface features are imprinted on eachfilm, the laminating material will be removed from the surface featuresand thus when the two films are joined there will not be any excessmaterial to seep into the open cavities. In certain embodiments, asdescribed above, the open cavities may be filled with a filler materialhaving a lower refractive index than the light guide material. Thisfiller material may be added prior to laminating such that the fillermaterial serves the added function of preventing any of the laminatingmaterial from seeping into and filling the cavities.

Other approaches are also possible. In an alternative embodiment, theturning features embedded in the light guide may be created by a singlecontoured film laminated to a planar film. For example, as shown inFIGS. 14-15, a light guide 203 may comprise a single contoured film 238laminated to the top, planar surface of light guide plate 223, such as aplastic or glass light guide. In the embodiment shown, the contoursurface of the film 238 is farther from the display panel than theplanar surface. Here, the turning facets may be protected by applying aplanar plastic cover layer 260 to the contoured surface of film 238. Forexample, the film 238 may comprise a plastic film, such as acrylic,polycarbonate, ZEONEX® or any other suitable plastic known in the art.The film 238 may be imprinted with a repeating surface relief structurecreated by embossing, injection molding or any other suitabletechnologies. The surface relief features 240 may comprise a pluralityof facets 242 and 244, which may be either be symmetric or asymmetric.The film 238 may then be attached or laminated to the top surface of alight guide plate 223 such that the embossed film 238 effectivelybecomes part of the light guide plate 223. Index matching adhesive maybe used. The imprinted surface relief features 240 remain as the top,exposed surface of the film 238. A cover layer 260 is then attached orlaminated to the exposed surface of the film 238. As discussed above, ifthe refractive index of both the film 238 and the cover layer 260 aresimilar, the surface relief features 240 are effectively embedded in thecomposite (single unitary) light guide 203.

As shown in FIG. 15, cavities (e.g., air pockets) 250, similar to thecavities discussed above, are created between the surface relieffeatures 240 and the cover layer 260. In use, plural light rays 5 fromthe light source 2 enter the light guide 203 at a light input surface233 and are guided along the length of the light guide via totalinternal reflection of the rays at the interface between the light guide203 and the surrounding air. When a light ray 5 strikes the light guidematerial/air interface created by one of the embedded cavities 250 at anangle greater than the critical angle for total internal reflection, thelight ray 5 will likewise undergo total internal reflection. However,because of the angle of air/light guide material interface created bythe facets 242 and 244 of the surface relief features 240, the totalinternally reflected light is turned through a large angle, usuallyninety degrees or greater and may then exit the light guide 203 via thelight output face 231 towards the display panel 4.

In certain embodiments, such as the cross-sectional view shown in FIG.16, the surface relief features 340 may be configured such that thecavities (e.g., air pockets) 350 in the light guide 303 have anasymmetrical shape. In particular, as shown, the side closer to thelight source 2 is different than the side farther from the light source2. For example, the steepness of the two facets 342 and 344 isdifferent. In FIG. 16, the surface relief features 340 comprises twoadjoining facets 342 and 344 wherein the first facet 342 is a short,steep facet and the second facet 344 is a vertical facet. Theasymmetrical shape of the cavities 350 reduces the length of the lightguide material/air interface and thereby reduces the detrimental Fresnelreflections that occur when light strikes the interface. The facets mayhave other angles as well, and may be shaped differently.

A further advantage of the embedded surface relief features is that theuse of embedded air/light guide material interfaces formed by thecavities 350 more efficiently relays light 5 from a side light source 2.For example, as shown in FIG. 17, when light rays 5 contained within acone having a half angle of approximately 30° propagate through thelight guide 303 and strike the light guide material/air interface at ancavities 350, some of the light 6 is turned down by total internalreflection, as described above, while some of the light 7 is refractedthrough the interface into the cavities 350. Here, the light 7 maypropagate through the cavities 350 until it strikes air/light guidematerial interface at the vertical facet 344. The light 7 is thenrefracted at this interface and is thereby quasi-collimated back intothe light guide material. If this light then strikes the air/light guidematerial interface at the surface of the light guide, the light 7 willbe totally internally reflected and remain in the light guide.Conversely, if the surface relief features did not comprise a cavitywith two embedded light guide-air interfaces, any light not totallyinternally reflected at the light guide material/air interface of thesurface relief feature would be refracted through the interface andescape the light guide. Thus, the efficiency of the light guide isimproved by embedding the cavities and providing a second air/lightguide material interface to prevent some refracted light from escapingthe light guide.

In alternative embodiments, as shown in FIG. 18, the turning facets 242and 244 may be coated with a reflective coating 280 such as silver orany other suitable metallic coating. The reflective coating 280 may alsoimprove the efficiency of the light guide, by causing any light thatwould have previously been refracted through the light guidematerial/air interface instead of being turned via total internalreflection to be reflected downward to the display panel by thereflective coating. In certain embodiments, as discussed above, thecavities 250 may also be filled with a filler material to providemechanical stability and strength to the structure. In certainembodiments, instead of applying a reflecting coating, the fillermaterial may be reflective.

The turning facets 242 and 244 may be any suitable shape for causing thelight to turn over a large angle at the light guide material/airinterface created by the surface features 240. In addition, as discussedabove, the size, shape, spacing or other characteristics of the facetsmay be varied to obtain uniform light extraction across the length ofthe light guide 203. In certain embodiments, as shown in FIG. 19, thesurface relief features 240 may comprise a plurality of multifacetedsurfaces 442 and 444 instead of the single faceted surfaces 242 and 244as shown in FIG. 15. The multifaceted surfaces may increase the angularrange over which the incident light is turned and thus increase theprobability that light turned by adjacent surface features 240, such asshown in FIG. 19, will overlap at the display panel 4, thus improvingthe uniformity of light incident on the display panel 4. This isespecially advantageous when the display panel 4 and the embeddedsurface relief features 240 are closely spaced such that the distance Dover which the turned light rays could spread is small. For example, asshown in FIG. 19, light rays 15 striking the multifaceted turningsurface 442 at different heights are turned by total internal reflectionover different angles depending upon the angle at which it strikes theturning surface.

In an alternative embodiment, as depicted in FIG. 20, the turningsurfaces 542 and 544 may alternatively comprise a single curved surface.The curved surfaces 542 and 544 may provide the same advantages asdiscussed above by varying the interface angle of the air/light guidematerial interface depending upon the location at which the incidentlight strikes the turning facet 542 and 544. This in turn increases theangular range over which the light is totally internally reflected andthereby increases the probability that light reflected by adjacentsurface features 240 will overlap as it strikes the display panel 4,thus improving the uniformity of the light incident on the display panel4.

In an alternative embodiment, as depicted in FIG. 21, the compositelight guide 603 may comprise a film 638 having a first planar surfaceand a second contoured surface with concave surface relief features 640extending across the length of a first side of the film and a plastic orglass light guide plate 623 having top and bottom planar surfaces. Thefilm 638 may be attached or laminated to the bottom surface of the lightguide plate 623 such that the planar surface of the film 638 is adjacentto the planar bottom surface of the light guide and the film 638effectively becomes part of the light guide plate 623.

The contoured surface of the film 638 faces away from the light guideplate 623 such that the concave surface relief features 640 remain onthe exposed surface of the film 638, also facing away from the lightguide plate 623. In certain embodiments, the concave surface features640 may be protected by applying a planar plastic cover layer 660 to thecontoured surface of film 638 to embed the surface features between thefilm 638 and the cover layer 660. As discussed above, if the refractiveindex of both the film 638 and the cover layer 660 are similar, thesurface relief features 640 are effectively embedded in the compositelight guide 603. Alternatively, the concave surface of the film 638 maybe attached or laminated directly to the array of display elements suchthat the concave surface features are embedded between the film 638 andthe array of display elements. The concave surface relief features 640may comprise a plurality of adjacent facets which may be either besymmetric or asymmetric. In the embodiment shown, the concave surfacerelief features 640 comprise sloping side walls or facets 642 and 644having the same slope although the slopes can be different in differentembodiments. These sloping side walls 642 and 644 are tilted such thatthe cavity 650 widens with depth into the film 638. Likewise, the edgesof each facet 642 and 644 nearest the display elements 4 are closer toeach other than the edges of each facet 642 and 644 furthest from thedisplay.

In certain embodiments, as depicted in FIG. 21, the surface relieffeatures 640 may be shaped and sized such that guided light propagatingthrough the light guide 603 will be totally internally reflected at theair/light guide material interface. In use, plural light rays 5 from thelight source 2 enter the light guide 603 at a light input surface 633and are guided along the length of the light guide via total internalreflection of the rays at the interface between the light guide 603 andthe surrounding air. When a light ray 5 strikes the air/light guidematerial interface created by one of the embedded cavities (e.g., airpockets) 650 at an angle greater than the critical angle for totalinternal reflection, the light ray 5 will undergo total internalreflection at the facet 642. Because of the angle of air/light guidematerial interface created by the facets 642 and 644 of the surfacerelief features 640, the total internally reflected light is turnedthrough a large angle, usually ninety degrees or greater (relative tothe light output face 631) and may then exit the light guide 603 via thelight output face 631 towards the array of display elements 4.

In alternative embodiments, as depicted in FIG. 22, the surface relieffeatures 740 may be shaped and sized such that guided light propagatingthrough the light guide 703 will be turned towards the array of displayelements by refraction of the light rays at the air/light guide materialinterface. Cavities (e.g., air pockets) 750, similar to the cavitiesdiscussed above, are created between the surface relief features 740 andthe cover layer 760. In the embodiment shown, the surface relieffeatures 740 comprise vertical sidewalls or facets 742 and 744, althoughthe shapes may be different in different embodiments.

In use, light rays 5 from the light source 2 enter the light guide 703at a light input surface 733 and are guided along the length of thelight guide via total internal reflection of the rays at the interfacebetween the light guide 503 and the surrounding air. When a light ray 5strikes the air/light guide material interface created by one of theembedded cavities 750, the light ray 5 will be refracted due to thechange in refractive index between the light guide and air. Because ofthe angle of air/light guide material interface created by the facet 742of the surface relief features 740, the light will be bent such that itexits the light guide 703 via the light output face 731 and is directedtowards the array of display elements 4.

A wide variety of other variations are also possible. Structuralfeatures may be added, removed, reordered, or rearranged. Differentstructural features may be substituted out. The type, arrangement, andconfiguration of the components may be different. Components may beadded or removed. Similarly, processing steps may be added or removed,or reordered. Also, although some embodiments are described as plates,these embodiments may otherwise comprise films or sheets. Additionally,the terms film and layer as used herein include film stacks andmultilayers. While these embodiments are discussed in the context of aninterferometric display, one of skill in the art will recognize that thetechnology is applicable in any directed-lighting solution includingroom lighting and display lighting for any of reflective, transmissiveand transflective technologies.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As is also stated above, it should be noted that the use ofparticular terminology when describing certain features or aspects ofthe invention should not be taken to imply that the terminology is beingre-defined herein to be restricted to including any specificcharacteristics of the features or aspects of the invention with whichthat terminology is associated. The scope of the invention is indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A light guide comprising: a cover layer having a planar surface; afilm having first and second surfaces, said first surface comprising aplurality of concave surface relief features and said second surfacebeing planar; and a light guide plate having top and bottom planarsurfaces, said light guide plate being thicker than said cover layer;wherein said film is disposed between said cover layer and said lightguide plate, wherein said film is disposed on said light guide platesuch that said planar second surface is adjacent said light guide plateand said concave surface relief features of said first surface face awayfrom said light guide plate; and wherein said cover layer is disposedadjacent said film such that the planar surface of said cover layer andthe concave surface features of said film form cavities between saidcover layer and said film such that light guided within the cover layer,light guide plate, and film is totally internally reflected from thecavities such that the light is no longer guided in the cover layer,light guide plate, or film.
 2. The light guide of claim 1, wherein thelight guide plate is disposed over an array of display elements, saidlight guide plate being closer to said display elements than said coverlayer.
 3. The light guide of claim 1, wherein the cover layer isdisposed over an array of display elements, said cover layer beingcloser to said display elements than said light guide plate.
 4. Thelight guide of claim 1, wherein the cover layer comprises an array ofdisplay elements.
 5. The light guide of claim 1, wherein the pluralityof concave surface features form elongate microprisms.
 6. The lightguide of claim 5, wherein the plurality of concave surface relieffeatures comprise at least two adjacent facets angled with respect toone another.
 7. The light guide of claim 5, wherein the plurality ofconcave surface relief features comprises two vertical facets.
 8. Thelight guide of claim 6, wherein the two adjacent facets comprise curvedsurfaces.
 9. The light guide of claim 5, wherein the microprismscomprise adjacent sides that are multifaceted.
 10. The light guide ofclaim 1, wherein the plurality of concave surface features have areflective coating thereon.
 11. The light guide of claim 1, wherein thecavities comprise air pockets.
 12. The light guide of claim 1, whereinthe cavities are filled with a filler material.
 13. The light guide ofclaim 1, wherein the filler material is reflective.
 14. The light guideof claim 1, wherein the film is disposed on the top planar surface ofthe light guide plate.
 15. The light guide of claim 1, wherein the filmis disposed on the bottom planar surface of the light guide plate. 16.The light guide of claim 1, wherein the cover layer is disposed over anarray of display elements.
 17. The light guide of claim 1, wherein thecover layer comprises a film having top and bottom planar surfaces. 18.The light guide of claim 1, wherein the film, cover layer and lightguide plate have the same index of refraction.
 19. The light guide ofclaim 1, wherein said light guide includes an edge through which lightcan be injected, said injected light being scattered out of said lightguide at said cavities.
 20. The light guide of claim 19, wherein theplurality of concave surface relief features comprise at least twoadjacent facets angled with respect to one another such that lightinjected through said edges is refracted at said cavities.
 21. The lightguide of claim 19, wherein the plurality of concave surface relieffeatures comprise at least two adjacent facets angled with respect toone another such that light injected through said edges is turned viatotal internal reflection at said cavities.
 22. The light guide of claim1, the cover layer further comprising: a viewing face positionedopposite said planar surface.
 23. The light guide of claim 22, theviewing face being planar.
 24. The light guide of claim 22, the viewingface being non-planar.